Morphological and structural study on GdSr/sub 2/RuCu/sub 2/O/sub 8/ melt-textured samples

Strongly anisotropic magnetic and superconducting properties have been recently observed to coexist in Gd1212 (GdSr/sub 2/RuCu/sub 2/O/sub 8/). Magnetic ordering appears to be due to Ru planes while Cu planes are correlated to the superconducting properties. The unavailability of single crystals makes relevant the fabrication of oriented samples of macroscopic size by melt texturing techniques. Then we have grown MTG samples starting from 1 cm diameter pellets. Gd1210 (GdSr/sub 2/RuO/sub 6/) is added, analogously to Y211 in YBCO MTG processes. Preliminary studies have been performed on Gd1212 powders to explore the range of temperatures and the reactions involved. XRD analysis shows that a certain degree of orientation is present in our samples. By Polarized Light Optical Microscopy we have observed large oriented domains of almost millimeter size. Larger domains are expected by optimization of growth parameters. Images show even a homogeneous distribution of Gd1210 precipitates with a mean size of a few micrometers. SEM and EDS analyses have also been performed, confirming optical observations. Resistivity measurements show a 12 K wide superconductive transition with T/sub c/ onset at about 40 K. Optimization of successive annealing treatments are expected to reduce this width.